Why is *salāta feminine? What was the original noun it is modifying?

OED traces the "salad" family of words (Portuguese salada, Fra. salate, Spa. ensalada, Ita. insalata etc.) to spoken Latin *salāta, from the verb salāre.

One notices that salāta as well as all its descendants are feminine. My question is, what is the feminine noun that the participle is implied to be modifying? It is a salted what?